Why France has avoided the cyclospora outbreak causing illness in the US

The US is grappling with a multi-state outbreak of explosive diarrhoea linked to the cyclospora parasite. Here is why France was spared.

The parasite has caused cases of an illness called cyclosporiasis across more than 30 US states. American health authorities believe outbreaks in at least five states are related to lettuce sold at Mexican-inspired fast food chain Taco Bell, but there may be other sources, according to the US Centers for Disease Control and Prevention (CDC).

So far this year, over 6,700 confirmed or probable cases of cyclosporiasis have been reported to the CDC. In Michigan, the hardest hit state, some 100 people have been hospitalised.

Cyclospora is not unique to the US and has shown up in Europe as well. So what are the chances a similar outbreak could hit France? Does the country's reputation for high quality food and local fruits and vegetables have a role to play in preventing an outbreak, given that cases in previous years in the US have also been linked to fresh produce? 

Ultimately, different importation and reporting practices on the two sides of the Atlantic play a role.

Dr Loïc Favennec, who leads a parasitology and mycology laboratory in Normandy, told The Connexion that cyclosporiasis remains rare in France.

"We have one or two cases where we have some questions, but otherwise, there is no apparent local transmission detected so far in France," said Dr Favennec, who is also the coordinator of the national cryptosporidiosis surveillance network.

The cyclospora parasite only infects humans, but inter-human transmission is highly unlikely. It needs time outside of the human body to become infectious, and is therefore transmitted via water used to irrigate fresh produce. Because of its long incubation period - sickness usually arrives after eight days versus just a few hours for bacteria - it is difficult to track quickly.

A big factor is from where each country imports produce. The US imports largely from Central and South America whereas France imports more from Africa and the EU. The parasite is particularly common in Central and South America, aided by the tropical climate and less widespread water treatment, according to Cleveland Clinic, an American academic medical center. 

In the US, reporting cyclosporiasis cases is less centralised than in France. Individual state health departments report their own numbers - using varying data collection methods - while the CDC compiles numbers nationwide. State-reported numbers for cyclosporiasis have therefore been higher than those the CDC reports. Adding to the complication is the fact that the US downgraded active surveillance for the parasite in July last year, following federal funding cuts.

In France, the reporting system is slightly different.

Only clusters of cyclosporiasis manifesting as foodborne illness outbreaks are subject to mandatory reporting. Sporadic cases are not. (In the US, most states report cases to the CDC - it is the state’s own laws that govern how reporting is done).

The search for cyclosporiasis is generally done in large private laboratory platforms, and most of these large platforms collaborate with the CNR, the Centre National de Référence, and its cyclosporiasis surveillance network, Dr Favennec said. While reporting is not mandatory, these laboratories will quickly send a case to the CNR, after anonymising patient data.

They will also send epidemiological information - like what the patient ate, whether they went to a pool, whether they drank non-potable water - that help identify how the contamination happened. The CDC collects similar exposure data.

One particularity of France, Dr Favennec explained, is that most cases do not come from transmission from Central or South American food products, the way it happens in the US. France may see 100-200 cases per year, with the majority thought to come from people who go to another country, catch cyclosporiasis, then return. Organised trips are often the culprit, he added.

Dr Favennec clarified that while the parasite can be transmitted via the irrigation of fresh food, it is a human parasite. That means it requires a person's stool to have contaminated a water supply which was then used to water crops.

"From a practical standpoint, there are very, very few affected people in France," he said. "So in the water, when you do tests on natural water in France, you never find cyclospora."

While cyclosporiasis is rare in France, since it is known to travel across borders it is always good to keep an eye out for symptoms. That is especially true for those travelling between the US and France.

Common symptoms of cyclosporiasis include watery diarrhoea and sometimes explosive bowel movements, according to the CDC. It is important to get a diagnosis as soon as possible, though that can be a challenge due to the lengthy incubation period before symptoms show up.

The good news is that cyclosporiasis is easily treatable with antibiotic prescription, Dr Favennec said.